It is asymmetric exposure that generates tilted latent image grating and then influence the shape of the groove during development. In order to simulate the formation of the grating,the asymmetric exposure and development model are introduced,with emphasis on that both the recording sources are on the same side of the substrate. The development of the groove is simulated and the in-situ monitoring curve in the fabrication of holographic grating is calculated. The results indicate that the exposure monitoring curve and development curve of asymmetric exposure are the same with that of symmetrical exposure. The groove will be tilted rectangular or asymmetric trapezoidal when the nonlinear effect is very remarkable or not so remarkable respectively. The asymmetry will be reduced when the nonlinear effect is restrained. A very good agreement between theory and experiment is obtained.